Do I have my first infection?

Brewed many stouts mostly using us04 dry yeast. Never noticed a vinegar smell or Taste but then again I don't usually check gravity for at least 2 weeks. Let it chill and check it again in a week could be something from the yeast. Also I hope you put some lactose in there with the cocoa powder. I made a chocolate milk stout for a friends wedding before and the cocoa powder adds a ton of bitterness if you don't have any lactose to back it up. Then again I also used a pound and a half of cocoa powder lol.

 

FWIW Acetobacter is the bacteria. It can make acetic acid, which tastes like vinegar.

 

RDWHAHB. Give it another week. It could be a combination of different things all working in tandem to create an aroma and flavor that your mind is deciphering as vinegar, but really isn't. 1 week in is too early to know much. There are fermentation characteristics that will eventually clean up like Diacteyl and Acetaldehyde, odd hop compounds that haven't smoothed out, alcohols that will smooth out, yeast in suspension. Give it another week to do its thing and taste it again. The other thing you have working in your favor is that fermentation produces CO2 which drives off the oxygen that the yeast don't absorb for fermentation, meaning you shouldn't have any oxygen for the Acetobacter to use to make the acetic acid. If the airlock were dry a week from now or the lid was off for an extended period of time, then that might be a likely culprit. If it is Acetobacter and it is making acetic acid, then there is nothing you can do to stop it at this point.

 

I agree with @jbakajust1. I'd wait and see. It really sounds kind of early for an infection. Also, acetic acid can/does exist in normal fermentations, at least in some... in hefeweizens it combines with isoamyl alcohol to form isoamyl acetate, which is where the banana flavor/aroma comes from.

 

You used 5ml before in a stout grain bill??

I typically don't add any acid to stouts or porters because the roasted dark grains really drop the mash ph on they're own. I am building from distilled water tho.

 

I'll typically just add pickling lime and baking soda to stouts because I actually need to raise the ph due to the roasted grains.

 

But the roasted grains are acidic too, so adding acid to an already acidic wort would compound the acidity.

 

Why did you want to increase the hardness?

Lactic acid shouldn't taste like vinegar. It's more of a clean tartness when there's enough to notice.

 

Are you using a water spreadsheet??

5ml of lactic acid seems like a lot in a roasted beer unless your adding a ton of baking soda also to boost ph.

 

Okay...yes, you definitely want a lot of alkalinity (not hardness per se, but now I see what you mean) for a stout, to counteract the acidity of the roasted grains. Which is what makes the lactic acid addition puzzling...it defeats the purpose of the baking soda.

 

I'm really thinking that this beer may be pretty low on the ph scale and that's what is giving you an impression of vinegar to your tastes. Perhaps the yeast kinda pooped out early due to being in an acidic environment?

Water is a really tricky thing. Especially on darker beers.

I'm assuming you don't have a ph meter?

7 days seems like a short time frame for acetic acid to form unless your fermenter was allowing lots of oxygen in for acetobacter to blossom?